Method and apparatus for inter-cell load balance in wireless communication system

ABSTRACT

A method and an apparatus for an inter-cell load balance in a wireless communication system are provided. The method of an inter-cell load balance of a first base station in a heterogeneous network wireless communication system including the first base station and a second base station includes configuring a first reserve area for the second base station, for the inter-cell load balance and controlling an inter-base station load balance according to the first reserve area.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of prior application Ser.No. 14/790,702, filed on Jul. 2, 2015, which has issued as U.S. Pat. No.10,547,550 on Jan. 28, 2020; which was based on and claimed priorityunder 35 U.S.C § 119(a) of a Korean patent application number10-2014-0082715, filed on Jul. 2, 2014, in the Korean IntellectualProperty Office, the disclosure of which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

The present disclosure relates to a wireless communication system. Moreparticularly, the present disclosure relates to a method and anapparatus for an inter-cell load balance in a wireless communicationsystem.

BACKGROUND

Typically, a wireless communication system has been developed to providevoice services while ensuring the mobility of users. However, thewireless communication system has gradually expanded to include a dataservice as well as a voice service and has been developed to provide ahigh speed data service. Though, since resources are lacking and usersdemand higher speed services in current mobile communication systems, animproved mobile communication system is needed.

To meet these demands, standardization of long term evolution (LTE) isbeing progressed by the 3rd generation partnership project (3GPP) as oneof the next generation mobile communication systems. The LTE implementshigh speed packet based communication with a transmission rate of up toabout several hundred Mbps. To this end, several methods are beingdiscussed, including reducing the number of nodes located on acommunication channel by simplifying a network architecture, makingwireless protocols more closely access a wireless channel to the maximumcapacity, and the like.

Specially, recently, a standardization for a time-domain inter-cellinterference coordination has been progressed, and thus a base stationshould effectively manage a user equipment (UE).

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present disclosure.

SUMMARY

Aspects of the present disclosure are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentdisclosure is to provide a method and an apparatus for effectivelymanaging a user equipment by a base station in a heterogeneous mobilecommunication system in which a macro cell and a small cell are mixed.

Another aspect of the present disclosure is to provide a method and anapparatus for improving a performance of a user equipment through aninter-base station load balance, in a heterogeneous network (HetNet)wherein a macro cell and a small cell share the same frequency.

In accordance with an aspect of the present disclosure, a method of aninter-cell load balance of a first base station in a heterogeneousnetwork wireless communication system including the first base stationand a second base station is provided. The method includes configuring afirst reserve area for the second base station, for the inter-cell loadbalance and controlling an inter-base station load balance according tothe first reserve area.

In accordance with another aspect of the present disclosure, a firstbase station for an inter-cell load balance in a heterogeneous networkwireless communication system is provided. The first base stationincludes a transceiver configured to transmit and receive with a randomnode of the wireless communication system and a controller configured tocontrol a first reserve area for the second base station, for theinter-cell load balance, and to control an inter-base station loadbalance according to the reserve area.

In accordance with another aspect of the present disclosure, a userequipment (UE) for performing a measurement report in a heterogeneousnetwork wireless communication system including a first base station anda second base station is provided. The UE includes a transceiverconfigured to transmit and receive with a base station and a controllerconfigured to receive a measurement report configuration message fromthe first base station, and to transmit the measurement report to thefirst base station according to the measurement report configurationmessage, wherein the measurement report configuration message isconfigured to enable the first base station to detect an entry into oran exit from a reserve area of the UE.

The first base station may determine whether the UE entry into or anexit from the first reserve area, according to the measurement reportconfiguration message received from the UE.

In accordance with another aspect of the present disclosure, a method ofreporting a measurement of a UE in a heterogeneous network wirelesscommunication system including a first base station and a second basestation is provided. The method includes receiving a measurement reportconfiguration message from the first base station and transmitting themeasurement report to the first base station according to themeasurement report configuration message. The measurement reportconfiguration message may be configured by a first base station suchthat the first base station detects entry into or an exit from a reservearea of the UE.

The first base station may determine whether the UE enters or exits thereserve area, according to the measurement report configuration messagereceived from the UE.

According to the present disclosure, a method of an inter-cell loadbalance and a method of an inter-cell interference adjustment in aheterogeneous network mobile communication system in which a macro basestation and a small base station are mixed are provided, and thus awireless resource efficiency of a network can be increased. In addition,according to the present disclosure, a load balance state of a networkcan adaptively provide inter-cell load balancing and inter-cellinterference adjustment.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the pre sent disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present disclosure will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a view illustrating a coverage area of a small cell, when anenhanced inter-cell interference coordination (eICIC) technique is usedaccording to an embodiment of the present disclosure;

FIG. 2 is a view illustrating a method of managing a cell area accordingto an embodiment of the present disclosure;

FIG. 3 is a view illustrating an area where an eICIC user equipment (UE)is placed according to each group, according to an embodiment of thepresent disclosure;

FIG. 4 is a block diagram of a macro cell base station according to anembodiment of the present disclosure;

FIG. 5 is a block diagram of a pico cell base station according to anembodiment of the present disclosure;

FIGS. 6A and 6B are views illustrating a method of managing a UE bydividing the UE into a macro cell expansion area (CRE) UE and a macronon-CRE UE, by a macro CRE UE managing unit, according to an embodimentof the present disclosure;

FIGS. 7A and 7B are views illustrating a method of managing the UE bydividing the UE into a pico CRE UE and a pico non-CRE UE by a pico CREUE managing unit, according to an embodiment of the present disclosure;

FIG. 8 is a view illustrating a state transition diagram used inmanaging a CRE state by a load balance determining unit of the macrocell base station according to an embodiment of the present disclosure;

FIG. 9 is a view illustrating a reference for determining whether a loadbalance is performed on an eICIC partner pico cell by a load balancedetermining unit of the macro cell base station according to anembodiment of the present disclosure;

FIG. 10 is a view illustrating a reference for determining whether aload balance on a macro cell is performed by a load balance determiningunit of a pico cell base station according to an embodiment of thepresent disclosure;

FIG. 11 is a flowchart illustrating an operation of the load balance bythe macro cell base station and the pico cell base station according toan embodiment of the present disclosure;

FIG. 12 is a flowchart illustrating a method of selecting a forcedhandover (HO) targeted UE by the macro cell base station according to anembodiment of the present disclosure;

FIG. 13 is a flowchart illustrating a method of selecting a forced HOtargeted UE by the pico cell base station according to an embodiment ofthe present disclosure;

FIG. 14 is a flowchart illustrating a method of expanding a coverage ofthe pico cell by shifting a HO trigger for the eICIC partner pico celltoward the macro cell in the macro cell base station according to anembodiment of the present disclosure;

FIG. 15 is a flowchart illustrating a method of reducing the coverage ofthe pico cell by shifting the HO trigger for the eICIC partner pico celltoward the pico cell in the pico cell base station according to anembodiment of the present disclosure;

FIG. 16 is a view illustrating an area where each type of UE may beplaced according to each group according to an embodiment of the presentdisclosure; and

FIG. 17 is a block diagram of a UE according to an embodiment of thepresent disclosure.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the present disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thepresent disclosure. In addition, descriptions of well-known functionsand constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of the presentdisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of the presentdisclosure is provided for illustration purpose only and not for thepurpose of limiting the present disclosure as defined by the appendedclaims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

In describing the various embodiments of the present disclosure,descriptions related to technical contents which are well-known in theart to which the present disclosure pertains, and are not directlyassociated with the present disclosure, will be omitted. Such anomission of unnecessary descriptions is intended to prevent obscuringthe present disclosure.

For the same reason, in the accompanying drawings, some elements may beexaggerated, omitted, or schematically illustrated. Further, the size ofeach element does not entirely reflect the actual size. In the drawings,identical or corresponding elements are provided with identicalreference numerals.

It will be understood that each block of the flowchart illustrations,and combinations of blocks in the flowchart illustrations, can beimplemented by computer program instructions. These computer programinstructions can be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, implement the flowchart block or blocks.These computer program instructions may also be stored in a computerusable or computer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer usable orcomputer-readable memory that implement the flowchart block or blocks.The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperations to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions that execute on the computer or other programmableapparatus provide operations for implementing the functions specified inthe flowchart block or blocks.

Each block of the flowchart illustrations may represent a module,segment, or portion of code, which includes one or more executableinstructions for implementing the specified function. It should also benoted that in some alternative implementations, the functions noted inthe blocks may occur out of the order. For example, two blocks shown insuccession may in fact be executed substantially concurrently or theblocks may sometimes be executed in the reverse order, depending uponthe functionality involved.

As used herein, the “unit” or “module” refers to a software element or ahardware element, such as a field programmable gate array (FPGA) or anapplication specific integrated circuit (ASIC), which performs apredetermined function. However, the “unit” or “module” does not alwayshave a meaning limited to software or hardware. The “unit” or “module”may be constructed either to be stored in an addressable storage mediumor to execute one or more processors. Therefore, the “unit” or “module”includes, for example, software elements, object-oriented softwareelements, class elements or task elements, processes, functions,properties, procedures, sub-routines, segments of a program code,drivers, firmware, micro-codes, circuits, data, database, datastructures, tables, arrays, and parameters. The elements and functionsprovided by the “unit” or “module” may be either combined into a smallernumber of elements, “unit”, or “module” or divided into a larger numberof elements, “unit”, or “module”. Moreover, the elements and “units” or“modules” may be implemented to reproduce one or more central processingunits (CPUs) within a device or a security multimedia card.

Hereinafter, a method of improving a performance of a user equipment(UE) through an inter-base station load balance, in a heterogeneousnetwork (HetNet) wherein a macro cell having a high power output and asmall cell having a lower power output share the same frequency isdescribed.

Typically, the macro cell has a coverage of a wide area because themacro cell has a relatively high power output. In contrast, the smallcell has a smaller coverage area narrower than the macro cell becausethe small cell has a relatively low power output. However, the smallcell has advantages it may be significantly more inexpensive.

The small cell is mainly used to cover a coverage hole which is notcovered by the macro cell, or used to absorb a load of the macro cell.However, since the coverage of the small cell is small, there is aproblem in which the small cell cannot effectively absorb the load ofthe macro cell.

3rd generation partnership project (3GPP) long term evolution (LTE)standard employs an enhanced inter-cell interference coordination(eICIC) or a time-domain ICIC technique to enable the small cell toabsorb the load of the macro cell effectively.

In a cellular wireless communication system, it is common that a cellhaving the highest downlink reception power is designated as a servingcell for a given user generally, and a corresponding user receives datatraffic from the serving cell. In contrast, the eICIC technique is atechnique for designating the small cell as the serving cell for a userwhen downlink reception power of the macro cell is larger than that ofthe small cell and for enabling the user to download a data traffic fromthe corresponding small cell.

FIG. 1 is a view illustrating a coverage of the small cell, when theeICIC technique is used according to an embodiment of the presentdisclosure.

Referring to FIG. 1, when the eICIC technique is used, a boundary of acoverage of the existing small cell 110 may be expanded to a boundary ofa reference numeral 120. As a result, the small cell absorbs more usersof the macro cell, and the macro cell's load may be distributed to thesmall cell.

Meanwhile, the users placed in the coverage of the small cell expandedarea 120 may have interference due to the macro cell having a signallarger than that of the small cell, and wireless channel quality may belargely degraded. Therefore, the users placed in the coverage of theexpanded small cell area 120 may experience difficulties in performing awireless communication.

In order to resolve the aforementioned technical problems, the 3GPP LTEeICIC technique provides an almost blank subframe (ABS) patterntechnique and a resource restriction technique.

According to the ABS pattern technique, the macro cell providesinformation referred to as an ABS pattern to the small cell experiencinginterference from a corresponding cell. The pattern information includes40 bits of a bit stream associated with an eICIC standard of 3GPP LTEfrequency division duplex (FDD), and refers to an existence of arestriction of transmission power (i.e., Tx power) of the macro cell,which is repeated every 40 ms period. For example, a value of a firstbit among 40 bits may refer to an existence of the transmission power(i.e., Tx power) of the macro cell in a first subframe. For example,when a corresponding value is 1(=ABS), the macro cell may reduce thetransmission power (i.e., Tx power), and when the corresponding value is0(=non-ABS), the macro cell may not be restricted by a specifictransmission power (i.e., Tx power).

Typically, according to the eICIC technique, since the UE placed in theexpanded coverage of the small cell has interference due to the macrocell, receiving wireless resources during only an ABS when the macrocell reduces the transmission power (i.e. Tx power) is advantageous insecuring wireless channel quality.

That is, the ABS pattern informs whether the transmission power (i.e.,Tx power) of the macro cell is reduced to the small cell, and thus is aenables the users placed in the expanded coverage of the small cell toperform a wireless communication stably.

Meanwhile, the resource restriction technique is a technique forincluding a user to measure a channel during only a specific subframe.

The resource restriction technique may include three types of patterns.

A first pattern includes 40 bit information, and restricts a subframewhen a user measures reference signal received power (RSRP) andreference signal received quality (RSRQ) for the serving cell anddetermines a radio link failure (RLF).

A second pattern includes a 40 bit information, and restricts a subframewhen a user measures RSRP and RSRQ for a neighbor cell.

A third pattern includes two pieces of 40 bit information. A first 40bit information may inform of a subframe used to measure first channelquality (i.e., channel quality indicator (CQI). A second 40 bitinformation may inform of a subframe used to measure second channelquality.

According to a normal eICIC technique, a network may enable the user todivide and measure channel quality in the ABS and channel quality of anon-ABS, using the third pattern. Through this, when the networkallocates a wireless resource to the user, the network may allocate aresource and determine a modulation and coding scheme (MCS) by applyingproper channel quality according to whether the ABS of a correspondingsubframe exists or not.

It is necessary to operate the third pattern effectively consideringthat the ABS pattern may change according to a time and a signalingoverhead that is incurred when the third pattern is transferred to theuser.

Meanwhile, the 3GPP LTE standard employs even a further eICIC (FeICIC)technique so as to provide a more effective load balance function.

In the FeICIC technique, the base station transfers inter-cellinformation to the UE through a signaling. Therefore, the FeICICtechnique removes interference by a cell-specific reference signal(CRS), which is generated from an interference cell, and, thus, theFeICIC technique improves channel quality.

Specially, when the macro cell implements the ABS, since channel qualityof the UE in the small cell may be improved, it is expected to increasethe coverage area of the small cell compared to the existing eICIC.

As described below, for convenience, the UEs are divided into threetypes and referred to as following.

-   -   legacy UE (or a first type UE): UE which does not support        eICIC/FeICIC technique.    -   eICIC UE (or a second type UE): UE which supports eICIC        technique.    -   FeICIC UE (or a third type UE): UE which supports FeICIC        technique.

An aspect of the present disclosure is to provide a method and anapparatus for an effective inter-cell load balance between a macro celland a small cell in a HetNet in which the macro cell and the small cellare mixed. The present specification is described based on a 3GPP LTEFDD wireless communication system, but the present specification may beapplied to other communication systems. In addition, the presentspecification is described based on an expansion of the coverage of thesmall cell in a network in which the macro cell and the small cell aremixed, but the present specification may be applied to another type ofcell configuration. In the present specification, for convenience, apico cell is described as an example of the small cell, but is notlimited thereto. An embodiment of the present disclosure may be appliedto a node such as a remote radio head (RRH) and a transmission point(TP).

FIG. 2 is a view illustrating a method of managing a cell area accordingto an embodiment of the present disclosure.

Hereinafter, a cell area expansion after cell area 120 of the pico cellcompared to a cell area expansion before cell area 110 of the pico cellis referred to as a cell expansion area or a cell reserve (CRE) area.

In this case, according to an embodiment of the present disclosure, thecell area expansion after cell area 120 may be the cell area expansionbefore cell area 110 is not included.

A UE which placed in a CRE of the pico cell or an area of a possiblecell expansion of the pico cell, and of which a serving cell is themacro cell is referred to as a macro CRE UE or a macro reserve area UE210.

Among UEs of which the serving cell is the macro cell, a UE excludingthe macro CRE UE is referred to as a macro non-CRE UE or a macronon-reserve area UE 220.

A UE placed in the CRE of the pico cell and of which a serving cell isthe pico cell is referred to as a pico CRE UE or a pico reserve area UE230.

Among UEs of which the serving cell is the pico cell, a UE excluding thepico CRE UE is referred to as a pico non-CRE UE or a pico non-reservearea UE 240.

In the method of managing the cell area shown in FIG. 2, the coverageexpandable area (i.e., the reserve area or the CRE area) in the picocell is operated as a shared cell area of the macro cell and the picocell, rather than a cell area of the macro cell or the pico cell itself.

In an embodiment of the present disclosure shown in FIG. 2, a UE thatbelongs to the reserve area is determined through a unique UE managementmethod. The macro cell determines a macro UE in the reserve area (i.e.,a macro CRE UE) and a macro UE which is not in the reserve area (i.e., amacro non-CRE UE).

In the same manner, the pico cell determines a pico UE in the reservearea (i.e., a pico CRE UE) and a pico UE which is not in the reservearea (i.e., a pico non-CRE UE).

According to an embodiment of the present disclosure shown in FIG. 2,when a load difference between the macro cell and the pico cell islarger than a threshold, a reserve area UE served by a serving cell maybe forcibly handed over to a cell having a lower load.

Meanwhile, since a cellular system applies a hysteresis to a handovergeneration condition so as to prevent rapid handovers, a shared cellarea is formed.

For example, a shared cell area formed in an area of the macro cell andthe pico cell becomes the macro cell area and becomes the pico cellarea, and, thus, when the UE moves in a corresponding area, a handoveris not generated. The shared cell area prevents the rapid handovers.However, there is a disadvantage because the UE cannot have an optimalcell as a serving cell based on a signal intensity. For example, thepico UE may be placed at a position where the received macro cellsignals are stronger as compared to the macro UE.

In the embodiment shown in FIG. 2, since a method of operating theshared cell area (or the reserve area) more widely, which is in theboundary of the macro cell and the pico cell, is used, there is aconcern that the UE may not have the optimal cell as the serving cellbased on the received signal intensity.

FIG. 3 is a view illustrating an area where the eICIC UE is placedaccording to each group, according to an embodiment of the presentdisclosure.

Referring to FIG. 3, the group includes four groups of the macro non-CREUE, the macro CRE UE, the pico non-CRE UE and the pico CRE UE. Thedefinitions of each group are described with reference to FIG. 2, andthus detailed descriptions concerning the definitions of each group areomitted.

An area overlapping a coverage area of the macro CRE and a coverage areaof the pico CRE UE corresponds to the reserve area (i.e., CRE area).

Referring to FIG. 3, for example, in a case of the UE, a macro UE 300may be placed in a position where the pico cell signal is receivedbetter than a pico UE 310. However, since an unnecessary wirelessresource waste is caused because of a degraded wireless channel quality,it may be preferable to swap the serving cells of the UEs 310 and 320.

Meanwhile, according to an embodiment of the present disclosure, an A3event of 3GPP LTE standard occurs to divide the reserve area UE. Inorder to reduce an RSRP information report (referred to as a measurementreport (MR) in 3GPP LTE) of an unnecessary UE, the UE transmits the MRonce when an A3 event entrance condition is satisfied.

However, since the same A3 event is used for determining handover (HO)with respect to another cell, the transmitting of the MR only once maycause degradation of the HO quality.

Hereinafter, according to an embodiment of the present disclosure, amethod of an effective inter-cell load balance between a macro cell anda pico cell in a HetNet system is described.

In another embodiment of the present disclosure described below, amethod of operating a wireless communication system capable ofmaximizing a load balance effect by minimizing wireless resource waste,maintaining handover quality and differentially operating an eICIC UEand an FeICIC UE is described.

System parameters related to an operation according to an embodiment ofthe present disclosure are described below.

-   -   eICIC ON/OFF parameter may turn on and off an eICIC operation.        -   CRE ON/OFF parameter is effective to only an eICIC ON, and            may turn on and off a pico cell coverage expansion function.    -   mobility load balancing (MLB) ON/OFF parameter may turn on and        off a forced handover function between the macro cell and the        pico cell.

FIG. 4 is a block diagram of a macro cell base station according to anembodiment of the present disclosure.

Referring to FIG. 4, the macro cell base station according to anembodiment of the present disclosure includes a macro CRE UE managingunit 410, a load calculating unit 420, a load information managing unit430, a load balance determining unit 440, a load balance performing unit450, an ABS rate determining unit 460, an ABS rate pattern generatingunit 470, and a wireless resource allocating unit 480.

The macro CRE UE managing unit 410 receives MR information from a UE ofwhich a serving cell is a macro cell, divides the UE into a macro CRE UEand a macro non-CRE UE, and manages the UE. In addition, the macro CREUE managing unit 410 outputs CRE UE information to transfer the CRE UEinformation to the load balance determining unit 440 and the loadbalance performing unit 450.

The load information managing unit 430 receives neighbor cell loadinformation from a neighbor base station and load information of themacro cell from the load calculating unit 420 of the macro cell thereof,and manages load information according to each cell. In addition, theload information managing unit 430 outputs the load information to theload balance determining unit 440 and the ABS rate determining unit 460.

The load calculating unit 420 receives scheduling information from thewireless resource allocating unit 480, and calculates a load of themacro cell. In addition, the load calculating unit 420 outputs thecorresponding result to the load information managing unit 430.

The load balance determining unit 440 receives the load information ofthe macro cell and the neighbor cell from the load information managingunit 430 and the CRE UE information from the CRE UE managing unit 410,determines whether the load of the macro cell is to be distributed tothe neighbor cell, and outputs load balance determination information tothe load balance performing unit 450.

The load balance performing unit 450 receives the CRE UE informationfrom the macro CRE UE managing unit 410 and the load balancedetermination information from the load balance determining unit 440,and performs a load balance operation. The load balance performing unit450 may output HO trigger change information to an eICIC partner picocell base station, and may transfer HO information to the UE to instructa performance of the handover. The HO trigger according to an embodimentof the present disclosure may refer to a reference line through which aHO from the macro cell base station to the pico cell base station orfrom the pico cell base station to the macro cell base station isperformed.

The ABS rate determining unit 460 receives the load information of themacro cell and the neighbor cell from the load information managing unit430, determines an ABS rate, and outputs ABS rate information to the ABSpattern generating unit 470.

The ABS pattern generating unit 470 receives the ABS rate from the ABSrate determining unit 460, determines the ABS pattern, and outputs theABS pattern to the wireless resource allocating unit 480 and the eICICpartner pico cell base station.

The wireless resource allocating unit 480 receives the ABS pattern fromthe ABS pattern generating unit 470, schedules a wireless resource inconsideration of the ABS pattern, informs of the scheduled wirelessresource to the UE, and outputs scheduling related information to theload calculating unit 420.

Meanwhile, in the above, the macro cell base station includes aplurality of other blocks that performs different functions, but are notlimited thereto. For example, the macro cell base station includes atransmitting and receiving unit that transmits and receives a signal toand from the UE or the pico cell base station. In addition, a controlunit may be implemented to perform all of the functions.

For example, the control unit may configure a variable reserve area forthe second base station, and may balance the load between the basestations according to the reserve area, for the inter-cell load balance.In this case, the UE of which the serving base station is the first basestation may be divided into a first base station reserve area UE and afirst base station non-reserve area UE and managed. The first basestation may be the macro cell base station and the second base stationmay be the pico cell base station.

In addition, the UE may include a first type UE which does not supportan eICIC function and a FeICIC, a second type UE which supports theeICIC function, and a third type UE which supports the FeICIC function.

In addition, the control unit may determine whether a forced handover isnecessary, and perform a handover on a random UE to the second basestation when the forced handover is necessary. In this case, the controlunit may determine whether the forced handover is necessary based on atleast one of an activation-or-not of an inter-cell interference controlfunction, an existence-or-not of an inter-cell interference controlpartner cell, an ABS rate that is currently being applied, and anexistence of a macro cell reserve area UE. In this case, the controlunit may control to select at least one UE for the forced handover,request a measurement report to the selected UE, and receive themeasurement report from the selected UE correspondingly to the request.

In addition, the control unit may select a UE positioned in a reservearea for a random second base station having a load is equal to or lowerthan a predetermined threshold value, as a UE for the load balance. Inaddition, the control unit may determine whether the reserve area is ina movable state when the forced handover is not necessary or themeasurement report is not received from the selected UE, and when thereserve area is in the movable state, the control unit may control tochange a handover reference line between the first base station and thesecond base station to shift the reserve area toward the first basestation or the second base station. In this case, the control unit maydetermine that the reserve area is in the movable state, when the eICICfunction and a CRE function is in an activated state. The control unitmay change the handover reference line by changing an offset value foran A3 event for the first type UE, the second type UE or the third typeUE. In this case, a movement range of the handover reference line forthe third type UE is wider than a movement range of the handoverreference line for the second type UE.

FIG. 5 is a block diagram of a pico cell base station according to anembodiment of the present disclosure.

Referring to FIG. 5, the pico cell base station according to anembodiment of the present disclosure includes a pico CRE UE managingunit 510, a load calculating unit 520, a load information managing unit530, a load balance determining unit 540, a load balance performing unit550, and a wireless resource allocating unit 560.

The pico CRE UE managing unit 510 receives MR information from a UEsserved by the pico cell, divides the UEs into pico CRE UEs and piconon-CRE UEs, and manages the UEs. In addition, the pico CRE UE managingunit 510 outputs CRE UE information to transfer the CRE UE informationto the load balance determining unit 540 and the load balance performingunit 550.

The load information managing unit 530 receives neighbor cell loadinformation from a neighbor base station and load information of thepico cell from the load calculating unit 520, and manages loadinformation according to each cell. In addition, the load informationmanaging unit 530 outputs the corresponding information to the loadbalance determining unit 540.

The load calculating unit 520 receives scheduling information from thewireless resource allocating unit 560, and calculates a load of the picocell. In addition, the load calculating unit 520 outputs thecorresponding result to the load information managing unit 530.

The load balance determining unit 540 receives the load information ofthe pico cell and the neighbor cell from the load information managingunit 530 and the CRE UE information from the CRE UE managing unit 510,determines whether the load of the pico cell is to be distributed to theneighbor cell, and outputs load balance determination information to theload balance performing unit 550.

The load balance performing unit 550 receives the CRE UE informationfrom the pico CRE UE managing unit 510 and the load balancedetermination information from the load balance determining unit 540,and performs a load balance operation. The load balance performing unit550 may output HO trigger change information to an eICIC partner macrocell base station, and may transfer HO information to the UE to instructa performance of the handover.

The wireless resource allocating unit 560 receives an ABS pattern fromthe eICIC partner macro cell base station, schedules a wireless resourcein consideration of the ABS pattern, informs of the scheduled wirelessresource to the UE, and outputs scheduling related information to theload calculating unit 520.

Meanwhile, in the above, the pico cell base station includes a pluralityof other blocks performs different functions, but they are not limitedthereto. For example, the pico cell base station may include atransmitting and receiving unit that transmits and receives a signal toand from the UE or the macro cell base station. In addition, a controlunit may be implemented to perform all of the functions.

Meanwhile, when the eICIC is in an off state or the CRE is in an offstate, the macro CRE UE managing unit 410 in the macro cell base stationmanages all UEs as the non-CRE UEs. Meanwhile, when the eICIC is in anon state and the CRE is in an on state, the macro CRE UE managing unit410 divides a UE satisfying three following conditions into the macroCRE UE or the macro non-CRE UE and manages the UE.

1. The UE has a corresponding carrier is a primary cell (PCell).

2. The UE does not have a guaranteed bit rate (GBR) bearer.

3. The UE is an eICIC UE or an FeICIC UE (i.e., not legacy UE).

The macro CRE UE managing unit 410 always manages a UE that does notsatisfy any of the three above-mentioned types as the macro non-CRE UE.

FIGS. 6A and 6B are views illustrating a method of managing the UEsatisfying the three above-mentioned conditions by dividing the UE intothe macro CRE UE and the macro non-CRE UE by the macro CRE UE managingunit according to an embodiment of the present disclosure.

Referring to FIGS. 6A and 6B, a UE that accesses to the macro cell forthe first time may be determined as the macro non-CRE UE.

The eICIC UE which is the macro non-CRE UE configures a cell individualoffset (CIO) value for at least one eICIC partner pico cell as(eICICBound−Δ/2) using an iICIC Bound value (=eICIC_B) corresponding toa corresponding pico cell. Each pico cell may have different eICICBoundvalues, and the eICICBound may refer to a boundary of the maximumcoverage area of the corresponding pico cell. A corresponds to an A3offset value generally used to prevent a HO ping-pong.

For example, when the eICIC UE is close enough to the eICIC partner picocell to satisfy a “macro RSRP+Δ≤pico RSRP+(eICICBound−Δ/2)” condition asshown as an arrow {circle around (2)} of FIGS. 6A and 6B, the eICIC UEperforms an MR report. In addition, the macro CRE UE managing unitdetermines the corresponding eICIC UE as the macro CRE UE.

The eICIC UE (i.e., the macro CRE UE) replaces the CIO value for alleICIC partner pico cells as an eICICCIO value corresponding to the picocell.

When the eICIC UE is close enough to the eICIC partner pico cell tosatisfy a “RSRP+Δ≤pico RSRP+eICICCIO” condition as shown as an arrow{circle around (4)} of FIGS. 6A and 6B, the eICIC UE performs the MRreport, and the corresponding UE performs the handover to the eICICpartner pico cell.

The eICIC UE configures one more A3 event, in this case, a hysteresisvalue is Δ/2, the A3 offset value is “Hysteresis−eICIC_B+eICICCIO”, and“reportOnLeave TRUE” is configured.

The eICIC UE reports an MR because an entering condition “(macroRSRP+(Δ/2−eICIC_B+eICICCIO)+Δ/2≤pico RSRP+eICICCIO)” is directlysatisfied for the added A3 event. When the eICIC UE is far enough fromthe eICIC partner pico cell to satisfy a leaving condition “(macroRSRP+(Δ/2−eICIC_B+eICICCIO)−Δ/2≥pico RSRP+eICICCIO)” as shown as anarrow {circle around (3)} of FIGS. 6A and 6B, the eICIC UE reports theMR again.

When the MR report is received, the macro CRE UE managing unitdetermines and manages the corresponding eICIC UE as the macro non-CREUE, and replaces and configures the corresponding eICIC UE as the A3event for the eICIC UE, which is the macro non-CRE UE.

The FeICIC UE (i.e., the macro non-CRE UE) configures a CIO value for atleast one eICIC partner pico cell as “(FeICICBound−Δ/2) using aFeICICBound value (=FeICIC_B)” corresponding to the corresponding picocell. Each pico cell may have different FeICICBound values, and theFeICICBound may refer to a boundary of a maximum coverage area of thecorresponding pico cell.

When the FeICIC UE is close enough to the eICIC partner pico cell tosatisfy a “RSRP+Δ≤pico RSRP+(FeICICBound−Δ/2)” condition as shown as anarrow {circle around (5)} of FIGS. 6A and 6B, the FeICIC UE performs anMR report. In addition, the macro CRE UE managing unit determines thecorresponding FeICIC UE as the macro CRE UE.

The FeICIC UE (i.e., the macro CRE UE) replaces the CIO value for alleICIC partner pico cells as an FeICICCIO value corresponding to the picocell. When the FeICIC UE is close enough to the eICIC partner pico cellto satisfy a “RSRP+Δ≤pico RSRP+FeICICCIO” condition as shown as an arrow{circle around (7)} of FIGS. 6A and 6B, the FeICIC UE performs the MRreport, and the corresponding UE performs the handover to the eICICpartner pico cell.

In the same manner, the FeICIC UE (i.e., the macro CRE UE) configuresone more A3 event, in this case, a hysteresis value is Δ/2, the A3offset value is “Hysteresis−FeICIC_B+FeICICCIO”, and “reportOnLeaveTRUE” is configured.

The FeICIC UE reports an MR because an entering condition “(macroRSRP+(Δ/2−FeICIC_B+FeICICCIO)+Δ/2≤pico RSRP+FeICICCIO)” is directlysatisfied for the added A3 event. When the FeICIC UE is far enough fromthe eICIC partner pico cell to satisfy a leaving condition “(macroRSRP+(Δ/2−FeICIC_B+FeICICCIO)−Δ/2≥pico RSRP+FeICICCIO)”, the FeICIC UEreports the MR again.

When the MR report according to the leaving condition is received, themacro CRE UE managing unit starts to determine and manage thecorresponding FeICIC UE as the macro non-CRE UE, and replaces andconfigures the corresponding FeICIC UE as the A3 event for the FeICIC UEwhich is the macro non-CRE UE.

Meanwhile, when the eICIC is in an off state or the CRE is in an offstate, the pico CRE UE managing unit in the pico cell base stationmanages all UEs as the non-CRE UEs. Meanwhile, when the eICIC is in anon state and the CRE is in an on state, the pico CRE UE managing unitdivides a UE satisfying three following conditions into the pico CRE UEor the pico non-CRE UE and manages the UE.

-   -   The UE has a corresponding carrier is a PCell.    -   The UE does not have a GBR bearer.    -   The UE should be an eICIC UE or an FeICIC UE (i.e., not a legacy        UE).

The pico CRE UE managing unit always manages a UE that does not satisfyany of the three above-mentioned types as the macro non-CRE UE.

FIGS. 7A and 7B are views illustrating a method of managing the UEsatisfying the three above-mentioned conditions by dividing the UE intothe pico CRE UE and the pico non-CRE UE by the pico CRE UE managing unitaccording to an embodiment of the present disclosure.

Referring to FIGS. 7A and 7B, a UE that accesses to the pico cell forthe first time may be determined as the pico non-CRE UE.

The eICIC UE (i.e., the pico non-CRE UE configures a CIO value for theeICIC partner macro cell as −MROCIO value. In order to prevent aconfusion by the same MROCIO variable applied to FIGS. 6A to 7B, a minussign is added.

When the eICIC UE is close enough to the eICIC partner macro cell tosatisfy a “pico RSRP+Δ≤macro RSRP+(−MROCIO)” condition as shown as anarrow {circle around (2)} of FIGS. 7A and 7B, the eICIC UE performs anMR report. In addition, the pico CRE UE managing unit may determine thecorresponding eICIC UE as the pico CRE UE.

The eICIC UE replaces the CIO value for the eICIC partner macro cell asthe −eICICCIO value corresponding to the corresponding macro cell. Inorder to prevent a confusion by the same eICICCIO variable applied toFIGS. 6A to 7B, a minus sign is added.

When the eICIC UE is close enough to the eICIC partner macro cell tosatisfy a “pico RSRP+Δ≤macro RSRP+(−eICICCIO)” condition as shown as anarrow {circle around (4)} of FIGS. 7A and 7B, the eICIC UE performs anMR report. In addition, the corresponding UE performs a handover to theeICIC partner macro cell.

The eICIC UE configures one more A3 event, in this case, a hysteresisvalue is Δ/2, the A3 offset value is “eICICCIO+MROCIO”, and“reportOnLeave TRUE” is configured.

The eICIC UE reports an MR because an entering condition “(picoRSRP+(−eICICCIO+MROCIO)+Δ/2≤macro RSRP−eICICCIO)” is directly satisfiedfor the added A3 event. When the eICIC UE is far enough from the eICICpartner macro cell to satisfy a leaving condition “(picoRSRP+(−eICICCIO+MROCIO)−Δ/2≤macro RSRP−eICICCIO)” as shown as an arrow{circle around (3)} of FIGS. 7A and 7B, the eICIC UE reports the MRagain.

When the MR report according to the leaving condition is received, thepico CRE UE managing unit determines and manages the corresponding eICICUE as the pico non-CRE UE, and replaces and configures the correspondingeICIC UE as the A3 event for the eICIC UE (i.e., the pico non-CRE UE).

The FeICIC UE (i.e., the pico non-CRE UE) configures a CIO value for theeICIC partner macro cell as −MROCIO value. In order to prevent aconfusion by the same MROCIO variable applied to FIGS. 6A to 7B, a minussign is added. When the FeICIC UE is close enough to the eICIC partnermacro cell to satisfy a “pico RSRP+Δ≤macro RSRP+(−MROCIO)” condition asshown as an arrow {circle around (5)} of FIGS. 7A and 7B, the FeICIC UEperforms an MR report. In addition, the pico CRE UE managing unitdetermines the corresponding FeICIC UE as the pico CRE UE.

The FeICIC UE (i.e., the pico CRE UE) replaces the CIO value for theeICIC partner macro cell as the FeICICCIO′ value corresponding to thecorresponding macro cell. In order to prevent a confusion by the sameFeICICCIO variable applied to FIGS. 6A to 7B, a minus sign is added.

When the FeICIC UE is close enough to the eICIC partner macro cell tosatisfy a “pico RSRP+Δ≤macro RSRP+(−FeICICCIO)” condition as shown as anarrow {circle around (7)} of FIGS. 7A and 7B, the FeICIC UE performs anMR report. In addition, the corresponding UE performs a handover to theeICIC partner macro cell.

The FeICIC UE (i.e., the pico CRE UE) configures one more A3 event, inthis case, a hysteresis value is Δ/2, the A3 offset value is“FeICICCIO+MROCIO”, and “reportOnLeave TRUE” is configured.

The FeICIC UE reports an MR because an entering condition “(picoRSRP+(−FeICICCIO+MROCIO)+Δ/2≤macro RSRP−FeICICCIO)” is directlysatisfied for the added A3 event. When the FeICIC UE is far enough fromthe eICIC partner macro cell to satisfy a leaving condition “(picoRSRP+(−FeICICCIO+MROCIO)−Δ/2≤macro RSRP−FeICICCIO)” as shown as an arrow{circle around (6)} of FIGS. 7A and 7B, the FeICIC UE reports the MRagain.

When the MR report according to the leaving condition is received, thepico CRE UE managing unit determines and manages the correspondingFeICIC UE as the pico non-CRE UE, and replaces and configures thecorresponding FeICIC UE as the A3 event for the FeICIC UE which is thepico non-CRE UE.

FIG. 8 is a view illustrating a state transition diagram used inmanaging a CRE state by the load balance determining unit of the macrocell base station according to an embodiment of the present disclosure.

According to an embodiment of the present disclosure, the CRE state mayinclude a CRE deactivated state and a CRE activated state.

The Referring to FIG. 8, when is the CRE is in the deactivated state,the CRE_status is 0. In contrast, when the CRE is in the activatedstate, the CRE_status is 1.

Initially, when the eICIC is in an on state and the CRE is in an onstate, the macro cell may start in the CRE deactivated state.

In the CRE deactivated state, to transit to the CRE activated state, thefollowing conditions should be simultaneously satisfied.

1. eICIC ON and CRE ON

2. CRE_status=0

3. The load of the macro cell should be equal to or larger than aspecific value.

4. A rate of the load occupied by an offloadable UE among loads of themacro cell should be equal to or larger than a specific value.

In the above conditions, the offloadable UE refers to a UE triggered tothe macro CRE UE by a pico cell having a current load that is lower thana specific value.

In some embodiments, the last condition may be replaced as thefollowing.

-   -   A rate of the offloadable UE among all macro cells should be        equal to or larger than a specific value.

Meanwhile, in a case of a transition from the CRE deactivated state tothe CRE activated state, the following operations are performed.

1. CRE_status=1

2. eICICCIO(pico)=MROCIO(pico), all eICIC partner pico cells areperformed.

3. FeICICCIO(pico)=MROCIO(pico), all eICIC partner pico cells areperformed.

4. An ABS rate is configured as a minimum value larger than 0.

Meanwhile, in order to enter the CRE deactivated state from the CREactivated state, at least one condition should be satisfied among thefollowing conditions.

1. eICIC OFF

2. CRE OFF

3. (CRE_status=1), the load of the macro cell should be equal to orlower than a specific value, and a sum of the load occupied by the picoCRE UE of the pico cell, which is the eICIC partner, should be equal toor lower than a specific value.

In some embodiments, the last condition may be replaced as thefollowing.

-   -   (CRE_status=1), the load of the macro cell should be equal to or        lower than a specific value, and a value obtained by dividing a        sum of the load occupied by the pico CRE UE of the pico cell        which is the eICIC partner by the load of the macro cell should        be equal to or lower than a specific value.

Alternatively, the last condition may be replaced as the following.

-   -   (CRE_status=1), the load of the macro cell should be equal to or        lower than a specific value, and a value obtained by dividing a        sum of the load occupied by the pico CRE UE of the pico cell,        which is the eICIC partner, by the load of the macro cell and        the pico cell should be equal to or lower than a specific value.

In addition, in order to be transited from the CRE activated state tothe CRE deactivated state, the following operations are performed.

1. CRE_status=0

2. eICICCIO(pico)=MROCIO(pico), all eICIC partner pico cells areperformed.

3. FeICICCIO(pico)=MROCIO(pico), all eICIC partner pico cells areperformed.

FIG. 9 is a view illustrating a reference for determining whether a loadbalance is performed to the eICIC partner pico cell by the load balancedetermining unit of the macro cell base station according to anembodiment of the present disclosure.

The operation may be performed in a specific period or non-periodically(e.g., when a specific event occurs), and may be performed only when aMLB is in an on state or when the eICIC is in an on state and the CRE isin an on state.

Referring to FIG. 9, when the load of the macro cell is equal to orlarger than a specific value TH_(M2), and the load of a specific picocell is equal to or lower than a specific value TH_(P2), the macro celldetermines that a load balance to a corresponding pico cell isnecessary.

FIG. 10 is a view illustrating a reference for determining whether aload balance on the macro cell is performed by the load balancedetermining unit of the pico cell base station according to anembodiment of the present disclosure.

The operation may be performed in a specific period or non-periodically(e.g., when a specific event occurs), and may be performed only when aMLB is in an on state or when the eICIC is in an on state and the CRE isin an on state.

Referring to FIG. 10, when the load of the pico cell is equal to orlarger than a specific value TH_(P3), and the load of the macro cell isequal to or lower than a specific value TH_(M3), the pico celldetermines that a load balance to a corresponding macro cell isnecessary.

FIG. 11 is a flowchart illustrating an operation of the load balance bythe macro cell base station and the pico cell base station according toan embodiment of the present disclosure. Specifically, FIG. 11 may be asequence of the operations performed by the load balance performingunits of the macro cell base station and the pico cell base station.

Referring to FIG. 11, a sequence of the operations performed by the loadbalance performing units of the macro cell base station and the picocell base station is described. Hereinafter, the load balance performingunit of the macro cell base station and the pico cell base stationperforms the operation of FIG. 11, but the present disclosure is notlimited thereto.

As described above with reference to FIG. 9, the load balancedetermining unit of the macro cell base station may determine that theload balance to the eICIC partner pico cell is necessary. As describedabove, when the load of the macro cell is equal to or larger than thespecific value TH_(M2), and the load of the specific pico cell is equalto or lower than the specific value TH_(P2), the load balancedetermining unit of the macro cell base station may determine that theload balance to a corresponding pico cell is necessary.

The load balance performing unit may distribute the load of the macrocell to the pico cell according to a load balance performing procedureshown in FIG. 11.

To this end, in operation 1105, the load balance performing unitdetermines whether the MLB function is activated (or on). When the MLBfunction is activated, in operation 1110, the load balance performingunit may request a MR to make at least one UE of the macro cell toreport RSRP information for neighbor cells including a serving cell onlywhen the UE satisfies a specific condition.

A method of selecting the UE to which the MR report is requested by themacro cell base station and the condition for report the MR aredescribed below with reference to FIG. 12.

In operation 1115, the load balance performing unit waits for the reportof the MR during a specific time and determines if a UE satisfies thecondition for the MR request. If a UE satisfies the condition for the MRrequest in operation 1115, the load balance performing unit performs aforced HO for all UEs or some UEs reporting the MR in operation 1120.The forced handover may refer to a process for a handover of UEs ofwhich the current serving cell is the macro cell base station to thepico cell base station which is the eICIC partner. Next, the loadbalance performing unit initializes count information (i.e., CNT) to 0,and ends the process.

When the MLB is not in an on state in operation 1105, there is no UEsatisfying the condition for the MR request or MR is not performedduring the specific time in operation 1115, the load balance performingunit performs operation 1125.

In operation 1125, the load balance performing unit determines whetherthe eICIC function is in an on state and the CRE is in an activatedstate. When the eICIC function is in an on state and the CRE is in anactivated state, in operation 1130, the load balance performing unitincreases the CNT value by 1.

Next, in operation 1135, the load balance performing unit determineswhether the CNT value is equal to or larger than a predeterminedreference value. When the CNT value is larger than the predeterminedreference value, the load balance performing unit shifts a handovertrigger toward the macro cell. This may indicate that a handover isperformed on even UEs adjacent to the macro cell toward the pico cell,by shifting a reserve area toward the macro cell, in selecting UEs forperforming the forced handover. A method of shifting the handovertrigger toward the macro cell by one operation is specifically describedbelow in FIG. 14.

Simultaneously, the load balance performing unit may initialize the CNTvalue as 0.

Meanwhile, when the eICIC is not in an on state in operation 1125, theCRE is in a deactivated state in operation 1125, or the CNT value islower than the specific value in operation 1135, the process is ended.

Meanwhile, the process of FIG. 11 may be applied to a case in which theload balance determining unit of the pico cell base station determinesthat the load balance to the eICIC partner macro cell is necessaryaccording to the condition of FIG. 10, by the same principle.

Referring back to operation 1105, the load balance performing unit ofthe pico cell base station determines whether the MLB function isactivated (or on). When the MLB function is activated, in operation1110, the load balance performing unit may request a Measurement Report(MR) to make at least one UE of the pico cell to report RSRP informationfor neighbor cells including a serving cell only when the UE satisfies aspecific condition.

A method of selecting the UE to which the MR report is requested by thepico cell base station and the condition for report the MR are describedbelow with reference to FIG. 13.

In operation 1115, the load balance performing unit waits for the reportof the MR during a specific time. In operation 1120, the load balanceperforming unit 550 performs a forced HO for all UEs or some UEsreporting the MR. The forced handover may refer to a process for ahandover of UEs of which the current serving cell is the pico cell basestation to the macro cell base station which is the eICIC partner. Next,the load balance performing unit initializes count information (i.e.,CNT) to 0, and ends the present process. Next, the load balanceperforming unit initializes count information (i.e., CNT) to 0, and endsthe present process.

When the MLB is not in an on state in operation 1105, there is no UEsatisfying the condition for the MR request in operation 1110, or any MRis not performed during the specific time in operation 1115, the loadbalance performing unit 550 performs operation 1125.

In operation 1125, the load balance performing unit determines whetherthe eICIC function is in an on state and the CRE is activated state.When the eICIC function is in an on state and the CRE is activatedstate, in operation 1130, the load balance performing unit increases theCNT value by 1.

Next, in operation 1135, the load balance performing unit determineswhether the CNT value is equal to or larger than a predeterminedreference value. When the CNT value is larger than the predeterminedreference value, the load balance performing unit shifts a handovertrigger toward the pico cell. This may mean that a handover is performedon even UEs adjacent to the pico cell toward the macro cell, by shiftinga reserve area toward the pico cell, in selecting UEs for performing theforced handover. A method of shifting the handover trigger toward themacro cell by one operation is described below with reference to FIG.15.

Simultaneously, the load balance performing unit may initialize the CNTvalue as 0.

Meanwhile, when the eICIC is not in an on state, the CRE is deactivatedstate, or the CNT value is lower than the specific value, the presentprocess is ended.

FIG. 12 is a flowchart illustrating a method of selecting a forced HOtargeted UE by the macro cell base station according to an embodiment ofthe present disclosure.

According to an embodiment of the present disclosure, a process shown inFIG. 12 may be performed by the load balance performing unit of themacro cell.

Referring to FIG. 12, for example, when any of the UEs of the macro cellis shifted toward the eICIC partner pico cell for a predetermineddistance, a UE placed in an area where a handover to the pico cell isperformed may be determined as the forced HO targeted UE.

In a case in which the eICIC is in an on state and the CRE is in an onstate is described first.

When the eICIC is in an on state and the CRE is in an on state, the areawhere the forced HO targeted UE is placed may be determined as the areashown in FIG. 12.

For example, since all legacy UEs 1210 are the macro non-CRE UEs, theload balance performing unit may configure the A3 event for all legacyUEs or some UEs sampled from all UEs. In this case, the load balanceperforming unit may maintain the CIO value as MROCIO, and may configurethe A3 offset as 0 dB.

In addition, in the case of the eICIC UE 1220, since the UE of the areashown in FIG. 12 is a subset of the macro CRE UE, the load balanceperforming unit may configure the A3 event for all macro CRE UEs or someUEs sampled from all macro CRE UEs, to only the eICIC UE which is themacro CRE UE. In this case, the load balance performing unit maymaintain the existing eICICCIO and may configure the A3 offset as 0 dB.

In addition, in the case of the FeICIC UE 1230, since the UE of the areashown in FIG. 12 is a subset of the macro CRE UE, the load balanceperforming unit may configure the A3 event for the FeICIC UEs or someUEs sampled from the FeICIC UEs, to only the FeICIC UE which is themacro CRE UE. In this case, the load balance performing unit maymaintain the existing FeICICCIO and may configure the A3 offset as 0 dB.

When the eICIC is in an off state or the CRE is in the off state, the A3event may be configured to all UEs or some UEs sampled from all UEs,regardless of the legacy UE 1210, the eICIC UE 1220 and the FeICIC UE1230.

As shown in FIG. 12, after the macro cell base station configures the A3event, the macro cell base station may wait for the MR during apredetermined period. When the number of the MRs from the UEs is largerthan a configured number, some UEs should be selected to be performedthe force HO.

To this end, the macro cell base station excludes a UE of which an RSRPof another cell except for the serving macro cell is larger than an RSRPof the pico cell of which the load is to be balanced, from the forced HOtargeted UE first. Next, the macro cell base station may previouslyselect a UE of which (PicoRSRP−macroRSRP) value is the largest among theremaining UEs as the forced HO targeted UE. When there are UEs of whichRSRO value differences are the same, the forced HO targeted UE may beselected in a sequence of the FeICIC UE, the eICIC UE and the legacy UE.

FIG. 13 is a flowchart illustrating a method of selecting a forced HOtargeted UE by the pico cell base station according to an embodiment ofthe present disclosure.

According to an embodiment of the present disclosure, a process shown inFIG. 13 may be performed by the load balance performing unit of the picocell.

Referring to FIG. 13, for example, when any of the UEs of the pico cellis shifted toward the eICIC partner macro cell for a predetermineddistance, a UE placed in an area where a handover to the macro cell isperformed may be determined as the forced HO targeted UE.

In a case in which the eICIC is in an on state and the CRE is in an onstate is described first.

When the eICIC is in an on state, the CRE is in an on state, and thecoverage of the pico cell is expanded enough to satisfy a“(eICICCIO≥MROCIO+Δ)” condition, the load balance performing unit maydetermine the area where the forced HO targeted UE is placed as the areashown in FIG. 13.

For example, since all legacy UEs 1310 are the pico non-CRE UEs, theload balance performing unit may configure the A3 event for all legacyUEs or some UEs sampled from all UEs. In this case, the load balanceperforming unit 550 may maintain the CIO value as −MROCIO, and mayconfigure the A3 offset as 0 dB.

In the case of the eICIC UE 1320, since the UE of the area shown in FIG.13 is a subset of the pico CRE UE, the load balance performing unit mayconfigure the A3 event for all pico CRE UEs or some UEs sampled from allpico CRE UEs, to only the eICIC UE which is the pico CRE UE. In thiscase, the load balance performing unit may maintain the CIO value as−eICICCIO and may configure the A3 offset as 0 dB.

In the case of the FeICIC UE 1330, since the UE of the area shown inFIG. 13 is a subset of the pico CRE UE, the load balance performing unitmay configure the A3 event for the FeICIC UEs or some UEs sampled fromthe FeICIC UEs, to only the FeICIC UE which is the pico CRE UE. In thiscase, the load balance performing unit may maintain the CIO value as−FeICICCIO and may configure the A3 offset as 0 dB.

When the eICIC is in an off state or the CRE is in the off state, the A3event may be configured to all UEs or some UEs sampled from all UEs,regardless of the legacy UE, the eICIC UE and the FeICIC UE.

At this time, in the case of the legacy UE, the load balance performingunit may maintain the CIO value as −MROCIO, and may configure the A3offset as 0 dB.

In addition, in the case of the eICIC, the load balance performing unitmay maintain the CIO value as −eICICCIO, and may configure the A3 offsetas 0 dB.

In addition, in the case of the FeICIC, the load balance performing unitmay maintain the CIO value as −FeICICCIO, and may configure the A3offset as 0 dB.

After the pico cell base station configures the A3 event as describedabove, the pico cell base station may wait for the MR during apredetermined period. When the number of the MRs from the UEs is largerthan a configured number, some UEs should be selected to be perform theforced HO.

To this end, the pico cell base station previously selects a UE havingthe largest quality, which is based on the “(macro RSRP−pico RSRP)”calculation, among the UEs reporting the MR. The pico cell base stationmay sequentially select the legacy UE, the eICIC UE and the FeICIC UEbased on the RSRP values.

FIG. 14 is a flowchart illustrating a method of expanding the coverageof the pico cell by shifting the handover trigger for the eICIC partnerpico cell toward the macro cell in the macro cell base station accordingto an embodiment of the present disclosure.

The handover trigger according to an embodiment of the presentdisclosure may refer to a reference line through which a HO from themacro cell base station to the pico cell base station or from the picocell base station to the macro cell base station is performed.

The process shown in FIG. 14 may be performed by the load balanceperforming unit of the macro cell base station.

Referring to FIG. 14, an increased value (or delta) shown in FIG. 14 mayoccur due to a base unit controlling the CIO. The delta may be adesignated value by 3GPP LTE standard, or may be a variable value by anoperator.

In operation 1410, the load balance performing unit determines whetherthe pico cell is not expanded enough to satisfy“(eICICCIO+Δ+delta≤eICIC_B)”. The eICICCIO may refer to a CIO valueconfigured to the eICIC UE. The eICIC_B may refer to a limit linethrough which the eICIC UE may be handed over to the pico cell.

When the condition “(eICICCIO+Δ+delta≤eICIC_B)” is satisfied, inoperation 1420, the load balance performing unit adds the delta to eachof the eICICCIO and the FeICICCIO. The FeICICCIO may be a CIO valueconfigured to the FeICIC UE. Referring to a reference numeral 1421, eachof the eICICCIO and the FeICICCIO shifts by the same delta value.

If the condition in operation 1410 is not satisfied, the load balanceperforming unit determines whether the condition“(FeICICCIO+Δ+delta≤FeICIC_B)” is satisfied in operation 1430. Thedissatisfaction of the condition “(eICICCIO+Δ+delta≤eICIC_B)” and thesatisfaction of the condition “(FeICICCIO+Δ+delta≤FeICIC_B)” may meanthat the eICICCIO should not become larger, but the FeICICCIO may becomelarger. That is, since the FeICIC UE has a function of removing the CRSfrom the macro cell, although the FeICIC UE is more adjacent to themacro cell as compared to the eICIC UE (i.e., although the handovertrigger is adjacent to the macro cell), the handover to the pico cell ispossible. Thus, in operation 1440, the load balance performing unitmaintains the eICICCIO value and adds the delta to only the FeICICCIO.The delta of operation 1420 and the delta of operation 1440 may be thesame or may be different. Referring to a reference numeral 1422, theeICICCIO does not shift and only the FeICICCIO shifts toward the macrocell base station by the delta.

Meanwhile, when all of the conditions of operation 1410 and operation1430 are not satisfied, it is impossible to expand the pico cellcoverage any more.

In this case, in operation 1450, the load balance performing unit maynot change the eICICCIO and the FeICICCIO.

FIG. 15 is a flowchart illustrating a method of reducing the coverage ofthe pico cell by shifting the handover trigger for the eICIC partnerpico cell toward the pico cell in the pico cell base station accordingto an embodiment of the present disclosure.

The process shown in FIG. 15 may be performed by the load balanceperforming unit of the pico cell base station.

Referring to FIG. 16, an increase value (or delta) shown in FIG. 15 mayoccur due to a base unit controlling the CIO. The delta may be adesignated value by 3GPP LTE standard, or may be a variable value by anoperator.

In operation 1510, the load balance performing unit may determinewhether the pico cell is sufficiently expanded enough to satisfy“(FeICICCIO+Δ−delta≥eICIC_B)”.

When the condition “(FeICICCIO+Δ−delta≥eICIC_B)” is satisfied, inoperation 1520, the load balance performing unit maintains the eICICCIOand subtracts the delta from the FeICICCIO. Referring to a referencenumeral 1521, only a value of the FeICICCIO shifts toward the pico cellbase station by the delta.

In contrast, if the condition “(FeICICCIO+Δ−delta≥eICIC_B)” is notsatisfied, in operation 1530, the load balance performing unitdetermines whether the condition “(eICICCIO−delta≥MROCIO)” is satisfied.The dissatisfaction of the condition “(FeICICCIO+Δ−delta≥eICIC_B)” andthe satisfaction of the condition “(eICICCIO−delta≥MROCIO)” may meanthat the eICICCIO and the FeICICCIO are the same and the coverage of thepico cell base station may be more reduced. Thus, in operation 1540, theload balance performing unit 550 subtracts the delta from each of theeICICCIO and the FeICICCIO. Referring to a reference numeral 1522, eachof the eICICCIO and the FeICICCIO shifts by the delta toward the picocell base station.

In addition, when all of the conditions of operation 1510 and operation1530 are not satisfied, it is impossible to reduce the coverage of thepico cell base station any more. Thus, in operation 1550, the loadbalance performing unit 550 may not change the eICICCIO and theFeICICCIO.

FIG. 16 is a view illustrating an area where the each type of UE may beplaced according to each group according to an embodiment of the presentdisclosure.

Referring to FIG. 16, four types of groups including the macro non-CREUE, the macro CRE UE, the pico non-CRE UE and the pico CRE UE areillustrated. The definitions of each group are described with referenceto FIG. 2, and thus detailed descriptions will be omitted.

Overlapping portions of a macro CRE UE coverage area 1610 a pico CRE UEcoverage area corresponds to the reserve area (i.e., the CRE area).

Referring to FIG. 16, the eICIC UE 1602 has a variable reserve areaaccording to a movement of the eICICCIO 1630 referring to a referenceline of the reserve area.

In addition, the FeICIC UE 1603 has a variable reserve area according toa movement of the FeICICCIO 1640 referring to a reference line of thereserve area.

Referring to FIG. 16, a movement range of the FeICICCIO 1640 for theFeICIC UE 1603 is wider than that of the eICICCIO 1630 for the eICIC UE1602. That is, since the FeICIC UE 1603 has a function of removing theCRS transmitted from the macro cell base station, the FeICIC UE 1603 mayhave a wider reserve area compared to the eICIC UE 1602.

FIG. 17 is a block diagram a UE according to an embodiment of thepresent disclosure.

Referring to FIG. 17, the UE of the present disclosure may include atransmitting and receiving unit 1710 and a control unit 1720.

The transmitting and receiving unit 1710 may transmit and receivesignals to and from a base station by forming a wireless channel.

The control unit 1720 controls a signal flow between blocks to allow theUE to operate according to an embodiment of the present disclosure.

The control unit 1720 may receive a measurement report configurationmessage from a macro base station or a small base station. In this case,the measurement report configuration message may be configured by afirst base station such that the first base station may detect anentrance or exit from a reserve area of the UE. Next, the control unit1720 may transmit a measurement result to the macro base station or thesmall base station after measuring according to the configuration of themeasurement report configuration message.

Accordingly, the first base station may determine whether the UE entersor exits the reserve area, according to the measurement reportconfiguration message received from the UE.

According to the above-mentioned embodiment of the present disclosure, amethod of an inter-cell load balance and a method of an inter-cellinterference adjustment in a heterogeneous network mobile communicationsystem in which a macro base station and a small base station are mixedare provided, and thus a wireless resource efficiency of a network canbe increased. In addition, according to the present disclosure, a loadbalance state of a network can be adaptively reflected by providing amethod of an inter-cell load balance and a method of an inter-cellinterference adjustment.

While the present disclosure has been shown and described with referenceto various embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present disclosure asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method by a first base station in aheterogeneous network wireless communication system including the firstbase station and a second base station, the method comprising:transmitting, to a plurality of user equipments (UEs) served by thefirst base station, a first configuration message, including firstinformation on a first offset value to trigger a transmission of a firstmeasurement report; receiving, from a UE among the plurality of UEs, thefirst measurement report based on the first configuration message;performing an interference cancellation operation for the UE, after thefirst measurement report is received; transmitting, to the UE whichtransmits the first measurement report, a second configuration messageincluding second information on a second offset value to trigger atransmission of a second measurement report; receiving, from the UE, thesecond measurement report based on the second configuration message; andstopping the interference cancellation operation for the UE, after thesecond measurement report is received, wherein an area for theinterference cancellation operation is determined based on the firstoffset value and the second offset value, and wherein a reserve area forload balance is determined based on the first offset value, the secondoffset value, and a type of a terminal, the type being associated withan interference cancellation function.
 2. The method of claim 1, whereinthe first measurement report is received in case that the UE moves outof a first boundary line associated with the first offset value, whereinthe second measurement report is received in case that the UE moves in asecond boundary line associated with the second offset value, andwherein the type of the UE includes one of a first type that does notsupport an enhanced inter-cell interference coordination (eICIC)function and a further eICIC (FeICIC) function, a second type thatsupports the eICIC function, and a third type that supports the FeICICfunction.
 3. The method of claim 2, further comprising: determiningwhether a forced handover of at least one UE of the plurality of UEs isnecessary; and performing the forced handover on the at least one UE toa second base station, when the forced handover is necessary, whereinthe at least one UE is located out of the first boundary line, andwherein the determining comprises determining whether a load balance isnecessary, based on at least one of an activation of an inter-cellinterference control function, an existence of an inter-cellinterference control partner cell, or an almost blank subframe (ABS)rate which is currently being applied.
 4. The method of claim 3, furthercomprising: transmitting, to the at least one UE, a third configurationmessage for triggering a transmission of a third measurement report;selecting the at least one UE for the forced handover; and receiving thethird measurement report from the at least one UE, based on the thirdconfiguration message.
 5. The method of claim 4, wherein the selectingcomprises selecting the at least one UE when the second base station hasa load that is equal to or lower than a predetermined threshold value.6. The method of claim 4, further comprising: determining whether areserve area of the first base station is in a movable state, when theforced handover is not necessary or the third measurement report is notreceived from the at least one UE; and changing, when the reserve areaof the first base station is in the movable state, a handover referenceline between the first base station and the second base station to shiftthe reserve area of the first base station toward the first base stationor the second base station.
 7. The method of claim 6, wherein thedetermining of whether the reserve area of the first base station is inthe movable state comprises determining that the reserve area of thefirst base station is in the movable state, when the eICIC function anda cell expansion area (CRE) function is in an activated state.
 8. Themethod of claim 7, wherein the changing of the handover reference linecomprises changing a third offset value of an A3 event for one of thefirst type, the second type and the third type, and wherein a movementrange of the handover reference line for a UE of the third type is widerthan a movement range of the handover reference line for a UE of thesecond type.
 9. A first base station in a heterogeneous network wirelesscommunication system, the first base station comprising: a transceiver;and at least one processor configured to: control the transceiver totransmit, to a plurality of user equipments (UEs) served by the firstbase station, a first configuration message including first informationon a first offset value to trigger a transmission of a first measurementreport, control the transceiver to receive, from a UE among theplurality of UEs, the first measurement report based on the firstconfiguration message, perform an interference cancellation operationfor the UE, after the first measurement report is received, control thetransceiver to transmit, to the UE which transmits the first measurementreport, a second configuration message including second information on asecond offset value to trigger a transmission of a second measurementreport, control the transceiver to receive, from the UE, the secondmeasurement report based on the second configuration message, and stopthe interference cancellation operation for the UE, after the secondmeasurement report is received, wherein an area for the interferencecancellation operation is determined based on the first offset value andthe second offset value, and wherein a reserve area for load balance isdetermined based on the first offset value, the second offset value, anda type of a terminal, the type being associated with an interferencecancellation function.
 10. The first base station of claim 9, whereinthe first measurement report is transmitted from the UE, in case thatthe UE moves out of a first boundary line associated with the firstoffset value, wherein the second measurement report is transmitted fromthe UE, in case that the UE moves in a second boundary line associatedwith the second offset value, and wherein the type of the UE includesone of a first type that does not support an enhanced inter-cellinterference coordination (eICIC) function and a further eICIC (FeICIC)function, a second type that supports the eICIC function, and a thirdtype that supports the FeICIC function.
 11. The first base station ofclaim 10, wherein the at least one processor is further configured to:determine whether a forced handover of at least one UE of the pluralityof UEs is necessary, and perform the forced handover on the at least oneUE to a second base station when the forced handover is necessary,wherein the at least one UE is located out of the first boundary line,and wherein the at least one processor is further configured todetermine whether the forced handover is necessary, based on at leastone of an activation of an inter-cell interference control function, anexistence-or-not of an inter-cell interference control partner cell, oran almost blank subframe (ABS) rate which is currently being applied.12. The first base station of claim 11, wherein the at least oneprocessor is further configured to: control the transceiver to:transmit, to the at least one UE, a third configuration message fortriggering a transmission of a third measurement report, select the atleast one UE of the plurality of UEs for the forced handover, andreceive the third measurement report from the at least one UE, based onthe third configuration message.
 13. The first base station of claim 12,wherein at least one processor is further configured to select the atleast one UE when the second base station has a load that is equal to orlower than a predetermined threshold value.
 14. The first base stationof claim 12, wherein the at least one processor is further configured todetermine whether a reserve area of the first base station is in amovable state when the forced handover is not necessary or the thirdmeasurement report is not received from the at least one UE, and whenthe reserve area of the first base station is in the movable state, theat least one processor controls to change a handover reference linebetween the first base station and the second base station to shift thereserve area of the first base station toward the first base station orthe second base station.
 15. The first base station of claim 14, whereinthe at least one processor is further configured determine that thereserve area of the first base station is in the movable state, when theeICIC function and a cell expansion area (CRE) function is in anactivated state.
 16. The first base station of claim 14, wherein the atleast one processor is further configured to change the handoverreference line by changing a third offset value of an A3 eventassociated with the third configuration message for one of the firsttype, the second type and the third type, and wherein a movement rangeof the handover reference line for a UE of the third type is wider thana movement range of the handover reference line for a UE of the secondtype.
 17. A user equipment (UE) for performing a measurement report in aheterogeneous network wireless communication system including a firstbase station and a second base station, the UE comprising: atransceiver; and at least one processor configured to: control thetransceiver to receive, from the first base station, a firstconfiguration message including first information on a first offsetvalue to trigger a transmission of a first measurement report, controlthe transceiver to transmit, to the first base station, the firstmeasurement report based on the first configuration message, control thetransceiver to receive, from the first base station, a secondconfiguration message including second information on a second offsetvalue to trigger a transmission of a second measurement report, andcontrol the transceiver to transmit, to the first base station, thesecond measurement report based on the second configuration message,wherein an interference cancellation operation for the UE is performedby the first base station based on the first measurement reportassociated with the first offset value, and stopped by the first basestation based on the second measurement report associated with thesecond offset value, wherein an area for the interference cancellationoperation is determined based on the first offset value and the secondoffset value, and wherein a reserve area for load balance is determinedbased on the first offset value, the second offset value, and a type ofa terminal, the type being associated with an interference cancellationfunction.
 18. The UE of claim 17, wherein the first measurement reportis transmitted from the UE, in case that the UE moves out of a firstboundary line associated with the first offset value, and wherein thesecond measurement report is transmitted from the UE, in case that theUE moves in a second boundary line associated with the second offsetvalue.
 19. A method of reporting a measurement of a user equipment (UE)in a heterogeneous network wireless communication system including afirst base station and a second base station, the method comprising:receiving, from the first base station, a first configuration messageincluding first information on a first offset value to trigger atransmission of a first measurement report; transmitting, to the firstbase station, the first measurement report based on the firstconfiguration message; receiving, from the first base station, a secondconfiguration message including second information on a second offsetvalue to trigger a transmission of a second measurement report; andtransmitting, to the first base station, the second measurement reportbased on the second configuration message, wherein an interferencecancellation operation for the UE is performed by the first base stationbased on the first measurement report associated with the first offsetvalue, and stopped by the first base station based on the secondmeasurement report associated with the second offset value, wherein anarea for the interference cancellation operation is determined based onthe first offset value and the second offset value, and wherein areserve area for load balance is determined based on the first offsetvalue, the second offset value, and a type of a terminal, the type beingassociated with an interference cancellation function.
 20. The method ofclaim 19, wherein the first measurement report is transmitted from theUE, in case that the UE moves out of a first boundary line associatedwith the first offset value, and wherein the second measurement reportis transmitted from the UE, in case that the UE moves in a secondboundary line associated with the second offset value.